The invention relates to an optical system which provides a collimated light beam, comprising a tubular holder, a semiconductor laser incorporated in the holder, and a system of lenses incorporated in the holder, the focus of which coincides with a laser element incorporated in the semiconductor laser.
An optical system of the above-mentioned kind is disclosed in U.S. Pat. No. 4,365,323, in particular FIG. 16. The semiconductor laser emits a strongly diverging beam of rays, in contrast with, for example, a HeNe laser. In order to obtain a parallel beam of rays when a semiconductor laser is used, the system of lenses must be positioned very accurately with respect to the semiconductor laser element, in which the focus of the system of lenses must be adjusted so as to be accurate within 1 .mu.m with respect to the laser element. The U.S. Pat. No. 4,356,323 shows a general arrangement but does not give any indication of how to obtain an accurate adjustment and a suitable structural configuration for the optical system.